The use of microwave energy for heating food products has become widespread. Heating by microwave energy of yeast-raised wheat-based food products such as bread and roll products has likewise become widespread. Applications of microwave energy for heating machine vendable sandwiches and breakfast type rolls are visible examples of this current use.
Problems have arisen with the use of microwave energy for heating traditional yeast-raised wheat-based food products such as bread and roll products. Traditional bread and roll products become impalatable after short exposures to microwave energy. The term palatable or palatability refers to the eating quality of food products. Palatable food products are agreeable to the taste and possess an appetizing appearance and texture.
Upon exposure to microwave energy, the crust of traditional bread and roll products becomes extremely tough. The crust of such microwave exposed products may become so tough that it is difficult to tear such products. The bread product itself may become soggy or develop hard lumpy portions. The crumb of the products becomes rubbery and gummy and is difficult to chew. Consequently, traditional bread and roll products, upon exposure to microwave energy, are not palatable.
An article entitled "Reformulating for Microwave," 25 Food Technology 921 (September 1971), describes the effect of microwaving on bread and suggests a reformulation for breads that are intended to be exposed to microwave energy. The article explains that the rate at which food products absorb microwave energy depends to a great measure on their moisture content. Products with high moisture contents, such as normally commercially baked sandwich rolls, heat very rapidly in a microwave oven. When filled sandwiches made with normal sandwich rolls are heated in a microwave oven, the rolls tend to overheat before the filling reaches serving temperature, substantially reducing the palatability of the overheated rolls.
Attempts have been made to deal with the problems associated with exposure of bread and roll products to microwave radiation, but have met with limited success. Methods for making bread and roll products for microwave applications have been tried using "rich" formulations. These "rich" formulations are low in water and high in sugar, shortening and egg. As suggested and described in the above-mentioned "Food Technology" article, buns prepared according to the "rich" formulation absorb microwave energy more slowly than do the traditional baked products, such as normal sandwich rolls, because of the lower moisture content of the "rich" products.
Pre-toasting of the bread and roll products has also been used to further reduce the water content in an attempt to alleviate the problems caused by exposure of the products to microwave energy. Use of day-old bread has also been suggested for improving a bread's ability to absorb microwave energy since day-old bread loses some of its natural moisture as it grows stale.
While minimal improvements in palatability have been obtained with the above-described reduced-moisture products, these improvements are in no way satisfactory because the reduced moisture products continue to evidence substantial reduction in palatability upon warming by exposure to microwave energy. The methods described above have additional drawbacks. Utilization of a relatively expensive "rich" formula adds cost to production. Pre-toasting adds an additional step to bread preparation, increasing production cost and handling time. Use of day-old bread disadvantageously requires storage of bread for at least a day until it becomes sufficiently "stale".
As described in application Ser. No. 407,621 filed on Aug. 12, 1982, it has been found that yeast-raisable wheat-based food products having improved resistance to deterioration in palatability upon exposure to microwave energy can be produced by use of yeast-raisable wheat-based formulations that include rice flour. It has now been found that the key to the effectiveness of rice flour is the rice starch of which it is composed and that certain other starches can be added to yeast-raisable wheat-based formulations to improve resistance to deterioration in palatability upon exposure of yeast-raised wheat-based food products to microwave energy.